Diaphragm valves for use in irrigation systems typically have an inlet opening, an exit opening and a diaphragm element having a seal positioned to selectively open and close against a generally cylindrical diaphragm seat to permit or block fluid flow through an opening of the diaphragm seat and thus from the inlet opening to the outlet opening. A control chamber is positioned on the opposite side of the diaphragm element from the seat to control the position of the seal of the diaphragm element. When the fluid pressure acting on the diaphragm element from the control chamber side exceeds the fluid pressure acting on the opposite side of the diaphragm element, the diaphragm element will be forced against the diaphragm seat to block fluid flow through the opening of the seat and thereby block fluid flow from the inlet opening to the outlet opening. Conversely, when the fluid pressure acting on the diaphragm element from the control chamber side is less than the fluid pressure acting on the opposite side of the diaphragm element, the diaphragm element will be forced away from the diaphragm seat to permit fluid flow through the opening of the seat and thereby permit fluid flow from the inlet opening to the outlet opening.
The seal of the diaphragm element often engages an annular face of the diaphragm seat when the diaphragm element is in its closed position to block fluid flow through the opening of the seat. Examples of such engagement between the seal and the face of the diaphragm seat are disclosed in U.S. Pat. Nos. 6,877,714 and 6,557,580. As the diaphragm element moves from its open position to its closed position, the flow area between the diaphragm seat and the seal continually decreases in correspondence with the position of the seal from the diaphragm seat until the seal is engaged with the diaphragm seat to block flow through the opening of the diaphragm seat. When the seal engages the diaphragm seat to block flow through the opening of the diaphragm seat, the abrupt change in the flow area between the seal and the diaphragm seat from greater than zero, immediately prior to engagement, and zero, at the time of engagement, can cause a sudden pressure spike greater than the upstream pressure. More specifically, the pressure spike in the upstream pressure can be caused as the motion energy in the flowing fluid is abruptly converted to pressure energy acting on the components of the diaphragm valve. This pressure spike can cause the diaphragm valve experience a water hammer effect, which can undesirably result in increased stress on the components of the diaphragm valve, as well as other components of the irrigation system, and can lead to premature failure of the components.
In order to control the pressure in the control chamber, a fluid entrance path and a fluid exit path to and from the control chamber are typically provided. The fluid entrance path may extend between the inlet opening and the control chamber, and may be continuously supplied with fluid from the inlet opening. The fluid exit path may extend between the control chamber and the outlet opening. A selectively actuatable control valve may be positioned to block fluid flow through the fluid exit path.
When the control valve is positioned to block fluid flow through the fluid exit path from the control chamber, the fluid entrance path continues to permit fluid to flow from the inlet opening to the control chamber, thereby causing fluid to accumulate in the control chamber. The diaphragm element has a larger surface area on the control chamber side than on the side facing the inlet opening. Thus, when the fluid pressure in the control chamber and inlet opening are generally the same, the operation of the fluid pressure in the control chamber acts on the greater surface area of the control chamber side of the diaphragm element and causes the diaphragm element to either shift from its open position to its closed position or to remain in its closed position.
When the control valve is positioned to permit fluid flow through the fluid exit path from the control chamber, fluid exits the control chamber at a faster rate than fluid enters the control chamber. This causes the fluid pressure acting on the control chamber side of the diaphragm element to decrease relative to the fluid pressure acting on the side of the diaphragm element facing the inlet opening. The fluid pressure in the inlet opening then causes the diaphragm element to move to its open position, whereby the seal of the diaphragm element is spaced from the diaphragm seat and fluid flow is permitted from the inlet opening, through the opening of the diaphragm seat and through the exit opening.
Dirt, grit and other debris are typically present in an irrigation system. The debris can have a detrimental effect on the operation of the diaphragm valve, particularly when the debris accumulates on various components within the diaphragm valve. For instance, debris can accumulate on the seal of the diaphragm element, and reduce the seal that can be achieved between the seal and the diaphragm seat. In some circumstances, the abrasive effect of the debris can degrade the seal. Debris can also clog the fluid entrance and fluid exit paths of the control chamber, which can result in improper operation of the diaphragm element and thus can lead to difficulties in opening and closing of the valve.
In order to reduce the presence of debris in the diaphragm valve, it has been known to position a cylindrical screen between the inlet opening and the control chamber of the diaphragm valve, as disclosed in U.S. Pat. No. 5,996,608. The '608 patent also discloses the use of a wiper that extends around the circumference of the cylindrical screen and is mounted for longitudinal reciprocation along the screen when the diaphragm valve is shifted between its open and closed positions to reduce accumulation of debris, and potential clogging, on the screen. The '608 patent further discloses a modified wiper element that is configured to spin freely around the filter screen. However, a freely spinning wiper element can disadvantageously harm the screen when the wiper element is rotating at high speeds due to the frictional contact therebetween. High speeds of the wiper element relative to the screen can occur, for example, during winterization when compressed air is blown through the system to flush out water. The high frictional contact between a freely spinning wiper element and the screen could generate sufficient heat to deform the screen and/or the wiper element.
During operation of the diaphragm valve, air can become trapped in the control chamber. The presence of excess air, a compressible fluid, in the control chamber can adversely effect the operation of the diaphragm valve, and in particular the shifting of the diaphragm element between its open and closed positions. For example, excess air in the control chamber can cause the diaphragm element to shift from its open position to its closed position more rapidly than intended, which can further exacerbate the water hammer effect discussed above. In order to permit for air to be removed from the control chamber, diaphragm valves have been provided with manually-operated bleed mechanisms that allow for a user to selectively vent air from the control chamber. However, when venting air from the control chamber, fluid is often expelled with the air. Depending upon the position of the passage through which the fluid and air is bled from the control chamber, an operator of the valve can be sprayed with fluid in the stream of air exiting the control chamber. For example, U.S. Pat. No. 6,079,437 discloses a control stem that is manually depressed to vent air from the control chamber. As shown in FIG. 2 of the '437 patent, an operator can be sprayed with fluid if present in the vented air, depending upon the position of the operator. The Toro Company, Minneapolis, Minn., has a valve with model no. 252-2506 that incorporates a bleed screw arrangement with a configuration that directs bled fluid from away from a user. However, the bleed screw arrangement of this valve does not sufficiently reduce the velocity of fluid exiting the control chamber, which can in some instances lead to undesirable spray.
The flow path that the fluid follows when the diaphragm valve is in its open position is generally from the inlet opening, past the opening of the diaphragm seat, and finally through the outlet opening. As the fluid follows this path, typical internal geometry of the diaphragm valve can cause very rapid acceleration and deceleration of the fluid. In particular, the geometry of the diaphragm seat can cause acceleration of the fluid as it approaches the opening of the diaphragm seat from the inlet opening. This can be due to the larger flow area of the inlet opening as compared to the flow area of the opening of the diaphragm seat, which can cause the fluid to rapidly accelerate as it approaches the opening in order to maintain incompressible fluid flow. Moreover, the geometry of the diaphragm seat can cause deceleration of the fluid at it exits the opening of the diaphragm seat and enters the outlet opening due to the smaller flow area of the opening of the diaphragm seat as compared to the larger flow area of the adjacent portion of the outlet opening. Rapid deceleration of the flow can cause the loss of energy in the fluid, which results in a pressure loss in the diaphragm valve.
In view of the foregoing deficiencies in existing diaphragm valves, there remains an unmet need for diaphragm valves having improved flow, including diaphragm valves configured to reduce debris in the flow paths, reduce the water hammer effect, reduce the energy lost during flow, and/or improve bleed operation.